The present invention relates to a cassette for delivering fluids, in particular dialysis fluids. The present invention also concerns a dialysis machine in which a cassette for delivering fluids, in particular dialysis fluids, can be accommodated and a method of delivering a medical fluid.
Generic cassettes for delivering fluids, in particular dialysis fluids, are known from International Patent WO 97/09,074 and are usually used as exchange items in dialysis machines. Such cassettes can fulfill the function of delivery of dialysis fluid with separation of media. A delivery chamber arranged in the cassette is driven pneumatically by a corresponding drive unit of the dialysis machine. It is also possible to use mechanically or hydraulically operated delivery chambers. The delivery chamber has a membrane that is activated by the drive unit and ensures that a separation between the media to be delivered and the working medium of the dialysis machine is guaranteed. The fluid flow in the cassette is controlled by means of pneumatically operated valves. To heat the dialysis fluid to be administered to the patient to the desired temperature level and keep it at that level, International Patent WO 97/09074 discloses trays on which the solution bags are stored during dialysis. For example, the trays are heated by heating cartridges which are in turn driven by a control unit of the dialysis machine.
With such an arrangement, it is a disadvantage that the heating of the dialysis fluids is uneven due to the one-sided storage on the heating trays and is associated with considerable heat loss. Furthermore, a separate heating step is necessary, which accordingly makes the design of the dialysis machine costly.
An object of the present invention is to create a device by which fluids, in particular dialysis fluids, can be easily and effectively heated and delivered.
This and other objects are achieved with a generic cassette having at least one area where fluid lines are arranged such that the medium in the lines can be heated to a predetermined set point by a heating device arranged outside the cassette. Cassettes according to the present invention have the advantages that the partial functions of delivering, metering/balancing, mixing, measuring, connecting and heating of medical fluids can be combined and performed in one unit. This greatly facilitates operation of the system and makes it more fail-safe by minimizing the steps that are subject to risk. The fact that the cassette according to the present invention is consistently connected in such a way that the media are separated permits sterile processing and thus reliably guards against the risk of infection.
According to a preferred embodiment of the present invention, a cassette includes a base structure with one or more films which cover at least part of the base structure and which are connected to the base structure. Walls of lines and a delivery chamber are formed by the base structure and the films. In the area of delivery chambers, the film is designed to be suitably elastic to serve as a membrane which is moved by the drive unit, e.g., by a piston pump, in accordance with a desired delivery height in the delivery chamber. The lines of the cassette which serve to guide the fluid flow are also bordered by the base structure and the film covering it. It is thus possible for only one wall of the lines or multiple walls to be formed by films.
In another embodiment of the present invention, a film extends on both sides of the base structure. This is advantageous especially in the area of the cassette, in that the lines are arranged in such a way that the medium in the lines can be heated to a predetermined set point by a heating device outside the cassette. In this case it is possible, with both sides of the film being used, to effectively heat both sides of the cassette and thus also the media flow, which is guided accordingly.
It is especially advantageous if one side of the base structure is completely covered with a film. In this case, the film in the area of the delivery chambers serves as an elastic membrane which causes the dialysis fluid, for example, to be delivered, while also permitting separation of media. In the area of the lines, the film forms one of the walls and permits especially effective and advantageous heat transfer into the medium in the line. Manufacture of the cassette is also simplified in this case, because the base structure has only recesses or indentations to form the delivery chambers or lines and then is covered with a film according to the invention, so that the recesses become delivery chambers and the channels in the base structure become lines. The film can be applied to the base structure relatively easily by welding or gluing.
According to a preferred embodiment of the present invention, two delivery chambers are provided. It is thus possible to achieve a relatively uniform flow through the cassette as well as an attached dialysis machine or patient, respectively, with alternating operation of the delivery chambers through a suitably coordinated drive unit. With a corresponding separation of the delivery chambers, it is likewise possible for one of the delivery chambers to be provided for a high pressure range and another to be provided for a vacuum or low pressure range, for example. Both delivery chambers can be bordered by the base structure in the cassette and by the film applied to it. Control of the media flow through the cassette and corresponding control of the delivery chambers can be achieved by line walls which are designed to be closed by applying a compressive force thereto. This compressive force may be applied pneumatically or mechanically by valve tappets, for example.
In another embodiment of the present invention, the lines are arranged in a spiral, at least in the heatable area of the cassette. This affords the advantage that a relatively great line length is arranged on a relatively small area of the cassette, which permits especially effective heating of the media in the lines. In addition to a spiral arrangement, other configurations having a high ratio of line length to line area, just as on achieving a turbulent flow even at relatively low flow rates.
It is especially advantageous if areas with a spiral arrangement of lines extend on both sides of the base structure. This makes it possible to heat the fluid to be heated first on one side of the cassette with a suitably arranged heating device and to keep it at the desired temperature in passing the other side of the cassette or to heat it further as needed.
The areas on different sides of the base structure may be connected to a hole provided in the base structure. It is thus possible to direct the media first to one side of the base structure and heat them, and then to direct them to the other side through the hole and heat them further, which is especially effective when the lines on both sides are arranged in the form of a spiral.
According to a preferred embodiment of the present invention, the base structure is made at least partially of plastic, which advantageously can be produced by injection molding methods, for example, in a variety of designs.
It is especially advantageous to provide the base structure with holders for mounting transducers, for mounting pressure, temperature and/or flow rate sensors. For example, temperature sensors may detect the temperature of a dialysis solution through the film and transmit the values to an analyzer unit. To regulate a temperature set point, the fluid delivery rate can be varied through the heated solutions or the heating power can be changed at a constant fluid delivery rate.
According to a preferred embodiment of the present invention, a line leading to the patient and a drainage tube which are undetachably connected to the cassette are provided. Thus, the cassette can be manufactured with these lines, while the assignment of the other connection elements of the cassette can be selected and implemented by a machine operator in accordance with the required dialysis method.
The present invention also relates to a dialysis machine, in particular for performing peritoneal dialysis, hemodialysis and plasma filtration methods, with a recess or device to accommodate a cassette according to the present invention, as well as having a pump unit for operating a delivery chambers of the cassette. To heat the cassette according to this invention, a heating device can be provided and arranged in the area of the recess or device for accommodating the cassette. It is thus possible according to the invention to use a new cassette with each patient, with the cassette being inserted into the dialysis machine or suitably arranged on it. Connecting the cassette to the dialysis machine in such a manner that the media are separated permits sterile processing and ensures aseptic conditions even when the dialysis machine is used by multiple patients. The risk of infection is effectively minimized since the cassette is a disposable unit which need not be reused.
On the whole, the invention is a simple, reliable and effective dialysis system where a machine operator need only arrange a cassette in the recess or device provided for it or connect the required lines after entering the desired set points. No separate arrangement of heating devices or elements is necessary.
In another embodiment of the present invention, the heating device has sheet or panel-type heating elements. This is especially advantageous in embodiments where a cassette has planar areas containing lines arranged in the form of a spiral, for example. In this case, especially effective heating of the media flowing through the lines is possible.
The heating device may extend to both sides of the recess or device for accommodating the cassette in such a way that the cassette can be heated on both sides. While requiring relatively little space, this embodiment case affords effective heating of the media to a desired set point even at high fluid rates.
The present invention also relates to a method for delivering, balancing, metering and heating a medical fluid, where a fluid delivered through lines and at least one delivery chamber is simultaneously receiving heat energy. This yields a method that is simple to carry out, where the partial functions of, for example, delivering, metering/balancing, mixing, measuring, connecting and heating medical fluids can be combined or performed in a compact manner.
It is especially advantageous if fluid is first sent through the delivery chambers and then heated in an area encompassing the lines. However, heating also may take place in the delivery chambers, alone or in combination with heating in the lines. Heating the fluid in the lines has the advantage that a great length of line can be accommodated as a result of the favorable arrangement of the lines in a relatively small area. This affords the possibility of heating the fluid effectively and in a controlled manner even at high flow rates.
Heating may take place in an area where the lines are arranged in spiral form. This yields an especially advantageous ratio of line length per unit of area, permitting especially effective heating.
In another embodiment of this invention, fluid first is passed through at least one delivery chamber of a cassette provided for delivering, balancing, metering and heating of fluid and is heated in lines on one side of the cassette, after which the fluid is transferred to the opposite side of the cassette and is heated further in lines on the opposite side. With such an arrangement, the fluid can be heated adequately even at high flow rates due to the relatively great line length extending on both sides of the cassette.
Additional advantages and details of the present invention are explained below on the basis of the embodiments described and illustrated in the figure.